Effect of V content and tempering treatment on microstructure and mechanical properties of the high strength steel TIG weld metal

Four kinds of welding wires with different V contents were used to weld the high strength steel plates by tungsten inert gas welding method. After welding, the weld metals of different welding wires were tempered at 640 ℃ for 2 h. The effects of V content and tempering treatment on microstructure and mechanical properties of weld metal were studied. The results show that for the as-welded and as-tempered weld metals, with the increase of V content, the strength increases and the elongation and impact energy decrease. Furthermore, after tempering treatment, M₂C carbide precipitated at the grain boundary of the V-free weld metal, while VC precipitated in V-bearing weld metals. During the post weld tempering process, the effect of dislocation recovery on matrix softening is stronger than precipitation strengthening of M₂C and VC. Therefore, under the combined effects of the two factors, the tempering treatment decreases the strength and improves the elongation and impact energy. The dispersed VC precipitates have the effect of hindering dislocation movement, which causes that the V-bearing weld metal retains high dislocation density after tempering. In practical application, V content and post weld tempering process should be selected reasonably according to the performance requirements of weld metal.